Many current vaccines employ attenuated microorganisms to induce protective immune responses against pathogens. Although these types of vaccines typically produce strong immune responses, there is a potential risk of infection due to the possibility of a reversion back to a virulent microoraganism, and therefore these vaccines may be contraindicated in some patient populations. Other vaccines that utilize recombinant antigens avoid the risk of infection, but generally produce weaker immune responses than live attenuated vaccines. Such weak immune responses with recombinant antigens are thought to be due to ineffective presentation of the antigens to the immune system. Thus, vaccine platforms that are better able to mimic the presentation of antigens to the immune system as occurs during natural infection are needed.
In recent years, virus-like particles (VLPs) or pseudovirions have been used to present antigens to induce an effective immune response. VLPs and pseudovirions structurally resemble naturally-occurring, infectious particles, but do not contain the necessary viral genetic information for replication. Immune responses to antigens presented on VLPs or pseudovirions are typically much greater than responses to soluble antigens. Although VLPs appear to be a useful platform for effectively presenting antigens to the immune system, efficient production of VLPs have proven difficult to achieve for some viruses. Furthermore, manipulation of viral capsid protein sequences and incorporation of foreign antigenic proteins or fragments into the viral particles often eliminates or reduces the efficient generation of intact VLPs.
Thus, there is a continuing need in the art to develop viable, safe vaccine platforms that effectively present antigens to the immune system without the associated risks of live attenuated vaccines. Furthermore, vaccine platforms in which any antigen of interest or multiple antigens from different pathogenic organisms can easily be incorporated are desirable.